Mineralization and pollution sources in the coastal aquifer of Lebna, Cap Bon, Tunisia

Abstract

This paper aims to determine the origin and processes of groundwater salinization in the Lebna coastal aquifer in northeastern of Cap Bon, Tunisia and to identify the main sources involved in the ecosystem alterations in this zone. To reach these goals, detailed geological and hydrogeological data were used in combination with geochemical and geophysical methods. The results show that the chloride, sodium and nitrate concentrations and electrical conductivity values exceed the World Health Organization WHO standard for drinking water. Further, the groundwater chemistry is classified into two main water facies: Na-Cl and Ca-Cl. Geochemical diagrams and the Saturation Index (SI) depicted two natural factors at the origin of salinization of the shallow aquifer, i.e., seawater intrusion by mixing processes and water-rock interaction by mineral dissolution and reverse cation exchange. Moreover, we showed that agricultural activities are the main source of NO3, SO4 and K ions and contribute to groundwater contamination with increasing chloride and nitrate concentrations. Based on geophysical results, we found that the seawater intrusion reaches 2.5 Km in the longitudinal direction from the sea inland and approximately 100 m in the aquifer depth.In conclusion, we were found several groundwater salinization sources in Lebna coastal aquifer, whereas, the principal mineralization origin is the seawater intrusion. This salinization influences the ecosystem change. Unfortunately, the groundwater in Lebna area is unsuitable for human drinking and irrigation uses.